MCR-01 Update - Engineering Matters _6

SAFETY
SPOT
Malcolm McBride
Airworthiness Engineer
or an aviation enthusiast of limited means, a job working for the LAA could be described as a Godsend; apart
F from the ‘total immersion’ in matters aeronautical there are other, perhaps many, less obvious benefits. One
of these is access to just about every airplane magazine going … free of charge. Of course there is a hierarchy,
you show me a place where Homo Sapiens have the whip hand where there isn’t, but even a lowly
Airworthiness Engineer can eventually get his/or her hands on these little plumbs of journalistic excellence. You
may wonder “where is this bloke going”? And I wouldn’t blame you … just bear with me a minute or two.
I’ve been getting moaned at by a few was a Tecnam Sierra. I must say MCR-01 UPDATE
sales types for mentioning their aircraft (looking over my shoulder!) the aircraft
I am very pleased to announce that Dyn
in Safety Spot; the general view seems was a pleasure to fly and it did
Aero have been able to provide a route
to be that, in the world of aircraft everything it said it would ‘on the can’
by which the remaining nine MCR-01
sales, nothing negative must be (no pun intended!). In fact, I think the
aircraft can get airborne. By the time
mentioned about a machine … or a performance was a little bit better than
that you are reading this I know that at
component … or an instrument … or book but, as I have already said, this is
least one of these aircraft will be back
anything else for that matter. I am not irrelevant. Why? Because Safety Spot is
a great reader of magazines and here to tell people the bad things about ‘in the air’. Regular readers will know
newspapers (except, of course, Light an aircraft, it’s not intended to be an that there are two big differences in the
Aviation) but, for the reason that I extended sales brochure. Its my job brackets that connect the tailplane to
mention above, I read more than my to pick holes in things and to let the fin on these aircraft; replacement of
fair share these days, and I am everybody know when somebody else the Type 2 brackets was fairly
beginning to detect a pattern, it’s has found a hole (and, possibly, fallen straightforward requiring only a change
probably nothing new … it’s just that through it). from an aluminium lug to one made of
I’ve just noticed it … never criticise, The cockpit of this aircraft was filled stainless steel. We were able to get
everything’s brilliant, all aircraft fly with gizmo’s, flat screen this and that, these aircraft flying again quite quickly
beautifully, even vices (vices!) are an all, in my opinion, a bit over the top, after Dyn Aero came up with some
essential part of an aircraft’s character but they looked great … if you like that stronger lugs. It has been more
and should be written about in glowing sort of thing. I was very concerned complicated to solve the problem of
terms. I understand the subtle feed- about the instrument layout and replacing, or modifying, the Type 1 lugs
back pressure that could cause this viz; general ergonomics of this machine, because the design of these lugs is
“you don’t write good stuff, and I’ll but you will have to wait for comments completely different. Dyn Aero has
send the boyz rawnd” … probably a bit about this as we need to fly the come up with a way of modifying the
strong, but you get the drift I’m sure. machine again (after we have read the tailplane so that it can accept Type 2
The problem with all this positive manuals!). I will just say this for now, lugs; unfortunately, this requires the
feedback is that the pressure to and please forgive me if I sound whole tailplane to be shipped back to
improve a product is reduced. Sure, a pompous, too many instruments may the factory to be completed, as I
bit of praise goes a long way, ask any lead the unwary into trouble … There have said, one owner has done this
school teacher, but if something’s not are many differences between flying a and is back in the air. The LAA has
right it needs to be pointed out. This is flight simulator in one’s study and the published an Airworthiness Information
especially true with regards to aircraft, real thing, and the biggest of these Leaflet (MOD/301/020 issue 2)
where lives are at stake. I got to fly an (many) differences is … you can get explaining the procedure.
aircraft the other day with Andy Draper, hurt in the real thing. More to follow. Dyn Aero has designed a ‘loop’ type
for an initial airtest for Permit, I do not For now, let’s look at a few things that support as an alternative to the factory
need to mention the aircraft type have been happening in the world of fix so that owners can upgrade their
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because this is irrelevant. Ok then, it stress and strain! tailplanes themselves; this modification
Engineering Matters ■ Light Aviation ■ June 2008 ■ 65
SAFETY SPOT ■ Malcolm McBride
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has been successfully load tested and,
at the time of writing, kits are being
supplied to customers. This latter
upgrade has not been approved by the
LAA as yet, we have only just received
the manufacturer’s fitting instructions;
we need to go through the procedure
on a Guinea Pig aircraft before this Note the multiple
modification is approved as there fatigue initiations along
appears to be some accurate the line of the weld.
fitting required.
Noselegs
Photograph: H. T. Consultants
We have had a few problems
associated with undercarriages over the
last year or so and I think that one or
two of these problems are worth
discussing here. Before I describe the
particular, individual items, I would like
to remind readers that the two bits of a
small aeroplane that have to work very
hard, pretty much every flight, are the
engine/propeller combination and the Pulsar Nose Undercarriage failure
undercarriage. Pilots often take a great
deal of interest in the former and
completely forget the latter; I can of the failed component which I am visibility, wet grass and a fickle wind
understand this, when you have just happy to share, note the multiple and … well, you could start breathing
spent all that money on the fancy fatigue initiations. This component had again when your wheels finally left the
flying suit, the last thing that you want been about to fail for some time and an ground. You’ve heard the terms ‘black-
to do is start grovelling around on the earlier Spot may have prevented an out’ and ‘red-out’, I’ve invented a new
ground looking at undercarriages. expensive (unexpected) propeller term, ‘blue-out’! The point is that each
There is also the phenomenon of change and a trailer ride home. aircraft has it’s difficulties of operation
‘out of sight … out of mind’ to be As a point of interest the Pulsar and these areas of difficulty need to be
considered. Regular readers will know aircraft was originally designed by Mark respected by the pilot. Very Light
that propeller problems feature quite Brown in the early 90’s; the aircraft was Aircraft, in particular, need to be
regularly in Safety Spot, I’ve got one or a derivative of his earlier single seater, respected on the ground.
two for you later in this issue, for now, the Starlight. I’ve had the pleasure of
let’s talk gear. discussing (and flying) Pulsars with
Mark and I recall him saying that the
Alpi
aeroplane was definitely not designed Some time ago I received a report of
Pulsar for rough field operation. some fairly serious cracking on the
We have just issued an Airworthiness Aircraft are generally designed to a main legs of a Pioneer 300 aircraft. This
Information Leaflet (AIL) requiring an set of requirements, for the sports aircraft had a fair number of hours on it
inspection of the nose undercarriage aviation community designers must and had recently been taken on by a
drag brace on Pulsar aircraft. This is in meet the requirements of CS-VLA, new, and no doubt very proud, owner.
response to an accident at Popham last there are stringent (and complicated) There were a number of issues about
year when the nose undercarriage tests required on undercarriage this particular undercarriage which were
failed during the landing; Popham’s components and these may include a unusual, and I won’t bore you with
runway is pretty smooth, the pilot had drop test. As I have said before, these but, when both legs end up
made a good landing, so the only real passing a drop test is one thing, cracking in the same place, at the same
damage was the loss of the propeller in-service conditions are another. In the time, then fatigue needs to be
and the failed undercarriage above case the failure was probably considered. Later legs are of a slightly
component. After an AAIB investigation, due to cyclic bending loads at, or about, different design, and Alpi has supplied
it was shown that the undercarriage the limit load for the material in the this customer with new main
drag brace support had failed at the component that failed. undercarriage legs free of charge,
point that it was welded to the engine I learnt to fly on taildraggers and I can which says a lot about Alpi’s
mount frame. I have discussed before remember the problem of, and definite commitment to continuing customer
how a material can change in the area need to, keep the stick hard back when support. Alpi has now called for a
of a weld; local, unresolved internal taxying. Manoeuvring on the ground repetitive inspection on these legs by
stresses coupled with a change in was a skill that had to be learnt … issuing a Service Bulletin; these cracks
temper can initiate fatigue foci. The throttle, stick, brakes; three things, two were entirely visible and should have
AAIB kindly supplied some photographs hands. Couple this with no forward been spotted earlier. Unlike the Pulsar
66 ■ Engineering Matters ■ Light Aviation ■ June 2008
Malcolm McBride ■ SAFETY SPOT
forks to be fitted at, or before, the next
annual inspection. This modification
increases the distance between the fork
and the runway by about an inch and, so
far, there have been no ‘dig-in’ incidents
involving modified nose forks.
The LAA has been holding back on
issuing an Airworthiness Information
Leaflet about this as one of our
members, Bill Knott, has been coming up
with a mod of his own. Bill’s mod uses a
UK manufactured fork which he has
designed to accept a big tyre (5.00 x 5),
this actually increases the fork-to-ground
dimension by two inches. This extra
ground clearance has to be a good idea
Photograph: Malcolm McBride
in the UK where the airfields can get a
bit on the bumpy side. The Bill Knott ‘big
tyre’ mod. has now completed flight
testing and is fully approved by the LAA;
if you’re a Vans owner you should have
received the AIL explaining your options
by the time you’re reading this. The only
Pioneer 300 Main Undercarriage Crack down side, as far as I see it, to Bill’s
mod. is that the spat will need to be
increased in size to accommodate the
aircraft above the Alpi Pioneer 300 was Later that month the National larger wheel … small beer, I suppose, if
designed as a tricycle type, and don’t Transportation Safety Board (Office of you’ve built your own aircraft; remember,
forget that it is a retractable. I note that Aviation Safety) published a study of a Vans recommend that their aircraft
the later Hawk has a beefed-up nose similar ‘flip-over’ type incident, involving should not be flown without a spat.
undercarriage which increases it’s max an RV-9A, that occurred in Alaska in These nosewheel mods only effect kits
all up weight a bit; this new August 2005. This study focussed on the supplied before February 2005, more
undercarriage is retrofitable onto the RV-9A case but also used data from information can be found on the Vans
older Pioneer 300’s. eighteen (yes, that’s 18) similar incidents website if you’re interested.
involving tricycle RV’s. Later, in Van makes some interesting points in
Vans September, another RV-9A ‘flipped-over’; his Service Bulletin and, to quote …
this time in the UK after a heavy landing. ”The nose gear on tricycle gear aircraft
Those that follow such things will Because of these incidents Vans has are not intended nor designed to
know that Vans aircraft have been sustain ‘landing’ loads. The nose gear is
issued a Mandatory Service Bulletin
suffering a few nose undercarriage
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(07-11-09) requiring updated nosewheel not a landing gear and is intended for
issues of their own; the LAA will be
issuing an AIL shortly describing
Bill Knott’s ‘Big Wheel Mod’ under development
changes that need to be made to Vans
nosewheel aircraft before the issue of
the next Certificate of Validity. Vans
aircraft are normally designed as either
tailwheel of tricycle configuration and
Vans always make the point that the
aircraft must be landed on the
mainwheels. The first major accident in
the UK involved an RV-7A (the ‘A’
means nose wheel type) one afternoon
in June 2007. The aircraft landed
normally with two occupants in good
weather. During the landing roll the
aircraft encountered a series of
undulations in the runway surface and
the nose wheel fork dug in, the aircraft
Photograph: Bill Knott
pitched over and came to rest on the
runway inverted. There is a good picture
of this unhappy situation in Ken’s
accident summary in the April edition of
Light Aviation, if you’re interested.
Engineering Matters ■ Light Aviation ■ June 2008 ■ 67
SAFETY SPOT ■ Malcolm McBride
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ground manoeuvring after touchdown
”
and deceleration. I suppose there may
be some comments about this
statement flying around the
aviation/design approval community
but, my advise to pilots, for what it is
worth, is to always be mindful of nose
undercarriage loads, for example:
Consider the aircraft’s centre of gravity,
work it out (?), try to avoid a very
forward CG condition; aircraft normally
fly more efficiently with aft. CG
anyway! Try to keep the stick back
whilst taxying, it’s a habit that has
been largely forgotten. Take a pride in
keeping the ‘nose up’ after landing for
as long as possible, get used to
Photograph: Bill Knott
looking down the side if you get a little
uneasy about lack of forward viz. Avoid
heavy braking, especially brake
‘pumping’, this just loads the
nosewheel up and can start oscillations
which, especially on bumpy ground,
Airmaster AP332 Ferrule Crack
can be difficult to manage. One last
thing regarding the aircraft’s operation,
a gearbox (various ratio’s often 1:2.27) highlights is that there is already a 25
and I am a little embarrassed to
which relates to a prop RPM of about hr/50 hr/ 100 hr inspection routine and
remind you of this, keep the tyres
2100 RPM. owners should be mindful that
pumped up!
The Airmaster 332 is a fully inspections called by component
One thing that has happened over
feathering propeller that uses an designers are particularly important and
the last few years is that builders are
electric motor to adjust the pitch of the shouldn’t be missed out.
putting bigger and bigger engines in
blades in flight, Airmaster us Warp
their aircraft; the difference between
Drive carbon fibre blades and, so far at
a Lycoming O-320 and an IO-360 is Woodcomp Effic
least, these blades have demonstrated
about 40 lbs and, when you take into
a good service history. Where possible, Last, but not least, please take a look
account the inevitable VP propeller …
the LAA always likes the manufacturers at the crack emanating from the rivet
Well I shall leave you to do the math.
to issue Service Bulletins to cover in- that was put in place to assist in
Talking about VP propellers…
service problems, we might back this securing a metal leading edge
up with an Airworthiness Information ‘protector’ on this woodcomp Effic
Airmaster AP332 Leaflet. I am in negotiation with the propeller. I do not intent to harp on
We have had a report of a cracked Airmaster factory at this moment about this bit of design brilliance …
ferrule on an Airmaster 332 that has regarding the cracked ferrule on the Suffice to say that there were two
been operating with a Jabiru engine Europa propeller, I know that Martin propellers with this improvement (?)
which we are a little concerned about. Eskildsen, the Airmaster boss, is in the operating in the UK on SportCruiser
Airmaster propellers are mostly fitted process of testing the hubs on Jabiru aircraft … They aren’t any more! With
to Europa aircraft which are generally engines. One thing that Martin that gem … Fair Winds! ■
powered by the Rotax 912/914
engines; these engines are fairly high
revving four-strokes and use a gearbox
to reduce propeller RPM. This gearbox
has the effect of damping out, or at
least limiting, peak loads from the
engine to the propeller hub. We have
had no reports of problems with the
AP332 coupled to a Rotax and only
one reported problem with the Jabiru.
The Jab engine doesn’t use a gearbox
Photograph: Graham Smith
and so the propeller hub takes all the
loads directly and runs at a generally
higher RPM. Peak power on the Jab
3300 (120 Hp) is at 3300 RPM, which Woodcomp ‘Effic’
is the prop speed; Rotax 912 peak metal leading
(80 – 100 Hp.) is 4800 RPM through edge failure
68 ■ Engineering Matters ■ Light Aviation ■ June 2008